The approaches described in this section could be pursued, but are not necessarily approaches that previously have been conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Computers and other devices can be enabled to communicate with each other through a computer network, such as a local area network (LAN), wide area network (WAN), or inter-network. In some networks, end stations, such as computers, are connected to intermediate network elements, such as routers, through communication links. The intermediate network elements also are connected to each other through communication links. Thus, one or more paths of communication links are established between end stations in a network.
A communication link, such as a cable, has a capacity. The capacity of a communication link describes the rate at which the communication link can transmit data. The rate at which data can be transmitted is often called “bandwidth.” For example, a communication link's bandwidth may be expressed as a number of bits per second. Some kinds of communication links have greater capacities than other kinds of communication links. The capacity of a communication link may be called the “size” of the communication link.
A single communication link may carry data transmitted to and from multiple end stations. For example, multiple end stations may be connected to single intermediate network element, which may be connected to a network through a single communication link. In such a configuration, all communication between any of the end stations and the network passes through the single communication link. Consequently, all of the end stations share the bandwidth of the single communication link. While a user of one end station is using a portion of the bandwidth, that portion is unavailable to users of the other end stations.
Users may enter into agreements with network service providers in order to obtain network connectivity. Such agreements are often called “service level agreements,” or “SLAs.” For example, a user may agree to pay a network service provider a specified amount of money per month in exchange for network access. Often, an agreement guarantees a minimum quality of service (QoS) and/or grade of service (GoS) to a user.
A QoS may specify several factors, such as the maximum probability that a data packet will be lost, and/or the maximum delay that a data packet will experience in transit. Generally, QoS factors relate to characteristics of data packets. In other words, QoS factors generally relate to traffic characteristics.
A GoS also may specify several factors, such as the maximum probability that a user's attempt to establish a communication session with the network will fail. A user's attempt to establish a communication session with the network may fail if a communication link's available bandwidth is less than the bandwidth that the communication session requires. In a converged network that provides packet voice service, a communication session is referred to as a “call.”
For example, when a user dials a telephone number on a telephone, the user initiates a call. When the user hangs up the telephone, the user terminates the call. For another example, when a user logs on to a network, the user initiates a call. When the user logs off of the network, the user terminates the call. The probability that an attempt to establish a communication session will fail is referred to as the “call blocking probability.” Thus, a GoS may specify a maximum call blocking probability. Generally, GoS factors relate to characteristics of calls.
As mentioned above, multiple end stations may share the bandwidth of a single communication link. Each such end station may be associated with a user who has been guaranteed a minimum QoS and a minimum GoS. The number of users that share a single communication link may fluctuate. For example, additional users may subscribe to the services of a network server provider that provides network access through the single communication link. Furthermore, the amount of bandwidth used by each user may fluctuate. When the number of users that share a current communication link increases, or when the combined amount of bandwidth used by the users increases, the bandwidth of the current communication link might become less than that necessary to guarantee the users the minimum QoS and the minimum GoS. In order to maintain this guarantee, the current communication link might need to be replaced with a communication link that has greater bandwidth.
Typically, bandwidth comes at a price. Communication links that provide greater bandwidth also cost more. For example, a T3 link provides greater bandwidth than a T1 link, but also costs more than the T1 link. To reduce costs, it is desirable to determine the minimum increase in bandwidth that is needed to support a specified increase in the number of users that share a communication link. The process of making this determination may be referred to as “link sizing.” Some previous approaches to making this determination exist.
Some approaches make the determination based solely on call characteristics. Call characteristics are a product of user behavior. For example, some approaches make the determination based solely on the average time between the arrivals of new calls on a communication link (the “inter-call arrival time”) and the average duration of calls on a communication link. Such approaches typically are used to determine the capacities of links in telephone networks. For each call currently on a communication link in a telephone network, a separate portion of the capacity of the communication link is dedicated exclusively to that call. Regardless of whether participants in a particular call are actively using the portion dedicated to the call, for example, by speaking, the portion is not made available to other calls during the particular call.
These call-characteristic-only-based approaches typically overestimate needed bandwidth when applied to networks in which a portion of overall bandwidth is not dedicated exclusively to a call. In Internet Protocol (IP) networks, the overall bandwidth of a communication link may be allocated among calls based on the calls' usage of the bandwidth at a given moment. For example, if a first call does not actively transmit data packets during a period of time, then, during that period of time, a second call may transmit data packets using the bandwidth formerly used by the first call. When the first call again actively transmits data packets, the second call may cease using the bandwidth being used by the first call. In this manner, less available bandwidth is wasted, and a greater number of calls may be supported. However, because call-characteristic-only-based approaches do not account for the sharing of bandwidth in this manner, call-characteristic-only-based approaches may determine an amount greater than the minimum amount of bandwidth that actually is needed to sustain a specified number of users.
Other approaches determine the needed increase in bandwidth based solely on traffic characteristics. For example, some approaches make the determination based solely on data burst characteristics during calls and how frequently data packets arrive during a burst on a communication link. A burst period is a period of time during which data packets arrive on a communication link relatively continuously. Such approaches typically are used to determine the capacities of links in IP networks. Examples of approaches that are based solely on traffic characteristics are discussed in A. I. Elwalid and D. Mitra, “Effective Bandwidth of General Markovian Traffic Sources and Admission Control of High Speed Networks,” IEEE/ACM Transactions on Networking, vol. 1, pp. 329-343, June 1993; D. Anick, D. Mitra, and M. M. Sondhi, “Stochastic Theory of a Data-Handling System with Multiple Sources,” The Bell System Technical Journal, vol. 51, pp. 1871-1894, October 1982; and M. Schwartz, Broadband Integrated Networks, Prentice Hall PTR, 1996.
These traffic-characteristic-only-based approaches typically overestimate needed bandwidth when applied to networks in which calls are discrete and of limited duration. In a telephone network, a particular user might establish a call that lasts for a limited duration, and then terminate the call. A substantial amount of time might pass before the particular user establishes another call. Because traffic-characteristic-only-based approaches do not account for the limited duration of calls in some networks, traffic-characteristic-only-based approaches may determine an amount greater than the minimum amount of bandwidth that actually is needed to sustain a specified number of users. Some of the shortcomings of traffic-characteristic-only-based approaches are discussed in M. Beshai, R. Kositpaiboon, and J. Yan, “Interaction of Call Blocking and Cell Loss in an ATM Network,” IEEE Journal on Selected Areas of Communications, vol. 12, pp. 1051-1058, August 1994.
The shortcomings of the approaches described above are at least partially a consequence of the limited scope of information that each such approach considers in making a determination of needed bandwidth. Based on the foregoing, there is a clear need for a method that considers a broader scope of information in determining the minimum amount of bandwidth needed on a communication link.